ergo-

Work; energy.

Greek ergon, work.

Ergonomics is the study of people's efficiency in their working environment, a practitioner being an ergonomist; an ergometer is an apparatus which measures work or energy expended during a period of physical exercise; an erg is a unit of work or energy in the older centimetre-gram-second system. However, ergosterol, a compound present in many fungi, derives instead from ergot, a fungal disease of cereals.